Burner control means



April 2, 1963 F. L. F. STEGHART ETAL 3,083,758

BURNER CONTROL. MEANS 2 Sheets-Sheet 1 Filed Jan. 5, 1960 IGNITION'TRANSFORMER ALARM l l l 7 FIGI April 2, 1963 F. 1 F. sTEGHART ETAL.3,083,758

BURNER CONTROL MEANS 2 Sheets-Sheet 2 Filed Jan. 5, 1960 ARM Arry .'r.

United States Patent Oiiice dfb Patented Apr. 2, 1953 .'idfdd BURNERQNTRL MEANS Fritz Ludwig lileiin Steghart, St. Aibans, Peter Leslie`Kershaw, Binner, and .lohn Percy Harvey, Burnham, England, asslgnors toThe llheostatie Company Liniited, Slough, England, a iiritish companyFiled dan. f3, iioil, Ser. No. 52th' Claims priority, application Greatbritain Eau. 6, i959 d iairns. (Ci. Mdm-2d) This invention concernsimprovements in fuel control means and has more particular reference tomeans for `controlling the supply of fuel to a burner and at the sametime controlling the ignition of the fuel. The embodiments to beparticularly described relate to oil burners, but it should beunderstood that the invention is equally vapplicable to other forms ofburners susceptible to the same type of control.

The safety regulations in many countries are very stringent as concernsoil burner control systems for central heating or the like, for it willbe understood that the situation might become dangerous if, for example,oil were pumped to the burner when it has not ignited. Thus in generalit is desirable for safety that, should there be a lfailure in any partof the system so that the various operations do not take place in theprescribed order, the apparatus must go `to an inoperative state if itis not possible to rectify the error by starting the cycle anew.

It is an object of the present invention, therefore, to provide a fuelcontrol system taking into account the -above safety precaution.

According to the presen-t invention there is provided fuel control meanscomprising a relay controlling two delay devices, the second of whichdelay devices is only energised after the first has been activated andsaid relay being de-energised in the run condition to de-energise thesecond delay means.

Very briefly, the preferred arrangement in accordance with the presentinvention comprises a sensitive relay having a .plurality of contactswhich control the various functions and the arrangement is that thermaldelays are heated (when the relay is energised) so as to provide fordelays before switching on the fuel supply and before going to thelock-out position, it being arranged that if llame appears at theappropriate time the relay is tie-energised so as to break the circuitto a thermal delay which controls lock-out, thereby preventing thelock-out. in contradistinction to the majority of relay-operated burnercontrols, the relay of the present invention is energised only duringthe initial start-up period and as soon as the burner is operatingsatisfactorily the relay goes to the released position.

in one arrangement in accordance with the'present invention three delaydevices may be provided, but again these are under the control of therelay with the exception that one of the delay devices remains energisedwhen the relay is de-energised. The chief function of the third delaymeans is to lprovide a purge time preventing immediate restart, therebyto increase the safety of the system. Moreover, in this embodiment thecontact `arrangement of the llame relay may be sirnpliiied so that itnow carries merely one make-before-break Contact.

It is extremely desirable in devices of this `general character that allthe contacts of the main relay should be tested during ordinaryoperation of the control means so as to ensure that the situation cannotarise that a pair of contacts may be defective but still allow thecontoller to operate without going to loch-out.

ln order that the invention may more readily be understood, cer-tainembodiments of the saine will now be described with reference to theaccompanying drawings, in which FIGURE l is a circuit diagram;

FEGURE 2 is a perspective view of a delay unit shown diagrammatically inFiGUREil; and

FGURE 3 is a circuit diagram of a second embodiment.

Referring to the drawings, it should be mentioned that the circlesappearing in certain of the leads (see FiGURE l) indica-te the externalconnections to the unit and that in the FiGURE 2 part of the unit itselfis shown but without the parts connected to such external connections.

Referring particularly to FIGURE l, the circuit comprises two leads Land N supplied with alternating current at mains voltage and frequency.Connected to the live mains lead L is a lead Ztl which passes viacontacts l and 2 of a thermal switch HL (controlling lock-out) to athermostat Tlz. The other side of this thermostat is connected via alead 2l to a resistance RD and thence to a bridge rectiiier BR. Theother side of the bridge rectitier BR is connected by a lead 22 tocontacts 8 and 7 of a `relay R which has its operating coil connectedacross the other two corners of the bridge rectifier BR. The contact 7is connected to the heater of the thermal switch HL and the other sideof this heater is connected via a resistance VR to the lead N of themains supply. The resistance VR is the voltage adjusting resistance forthe circuit.

In the circuit so far described, if the thermostat Th closes to call formore heat, the bridge rectifier BR is energised and the relay R pulls into close the contact S upon a contact 6 and to break the Contact 7 fromthe contact S. The eiect of closing the contacts 6 and S is to bring aresistance RR into series between the lead 2'?. and the resistance VR,this resistance RR having a resistance equivalent to that of thelock-out heater HL. Consequently the relay R remains energised and it isobvious that the contacts ti and 8 close before the contacts 7 and 8open so that although the circuit to the heater of the thermal switch HLis broken, the relay R is not simultaneously de-energised.

The coil of the relay R is in parallel with a photo-resistive type ofphoto-cell ld and it will be clear that if there is light on thephoto-cell, for example, if for any reason the furnace is incandescent,the relay R will not pull in as its coil will be shunted by thephoto-cell F. Similarly the relay R will not pull in if there is an opencircuit ilthe resistance RD or in the heater of the thermal switch rhelead 2l between the thermostat Th and the resistance RD is connected toa lead 23 which terminates at a contact l1 which makes with a contact 12of the relay R when the relay pulls in and this contact l2 is connectedby a lead 2dto an ignition transformer T which has its other sideconnected to the neutral lead N. Thus as soon as the relay R pulls inthe ignition is started.

The lead 23 is also connected to a contact i3 or a thermal switch HM(for motor control) which, in the cold condition, makes with a contactid connected to a contact 9' of the relay R. When the relay R pulls in,this Contact 9 is connected to a contact l@ and thence to the heater ofthe thermal switch HM which has its other side connected to theresistance VR. Thus the heater-of the thermal switch HM is energised.

The relay contact 'i is connected to a relay Contact 5 of the relay Rand, on energisation of the relay, this contact 5 makes with a contact iconnected via a lead 2t? te a Contact i4 of the thermal switch HM andthence via a `resistance RM to the Contact itl. Thus when the relay R isenerglsed, the heater of the thermal switch HL is energised at a lowrate via the following circuit: lead 2.3, contacts i3 and l5, contacts 9and ftd, resistance RM, lead 2o, contacts l and 5, the heater coil ofthe thermal switch HL, resistance Vl?. and the neutral lead.

spoof/e After a pre-ignition period of some l0 to l2 seconds, thethermal switch HM will operate and `will switch the Contact 13 from thecontact 15 to the contact 14 thus connecting the lead 23 to the lead 26and applying full power through resistance VR to the heater of thelthermal switch HL. The lead Z6 is connected to a lead 27 und thence toa motor M for the oil pump, this motor having its other side connectedto the neutral supply line so that on operation of the thermal switch HMfull mains voltage is applied to the rnotor M which is thus switched onto supply the fuel. At the same time the circuit to the thermal switchHM through the contact is broken and is reestablished through thecontact 14 and the resistance RM so as to supply a reduced amount ofcurrent to the heater oi this switch but just suiiicient to maintain thesame energised.

When flame is established, the resistance of the photocell P is reducedto shunt `the coil of the relay R, thus causing the relay to open tobreak the ignition circuit at the contacts 1-1 and 12 and to break thecircuit to the thermal switch HL at the contacts 4 and 5. The circuit isnow in the normal run condition.

If, however, the flame is not established the relay will remainenergised and Iafter approximately l0 seconds the thermal switch HL willbe energised to break the contacts 1 and 2 and make the contacts 1 and3, thus switching in an alarm A and simultaneously de-enerising therelay R and, therefore, stopping the motor M and the ignitiontransformer T. The thermal switch HL has to be reset manually and thiscannot be accomplished until the heater of the switch HL has cooleddown, such cooling taking over 60 seconds.

If at any time during the normal run the ilame should fail or tan opencircuit should occur in the photo-cell leads, the shunt resistance isremoved `from the coil of the relay R which will pull in to restore theignition circuit and energise the heater for the lock out switch HL,whereby the equipment recycles or goes to lock-out if the flame is notre-established within the correct time. Similarly also if the thermostatTh opens, the power supply to the motor M is broken and the circuit isswitched oil.

FIGURE 2 illustrates the thermal switches HL and HM, these switchesbeing designed for attachment by means of a footplate to a relay unitincorporating the relay R and the rectifier BR. It is not necessary toillustrate the relay R which is conventional, except in so far as thecontacts 6, 7 and 8 are concerned where the arrangement is that in thede-energised condition of the relay the contacts 7 and are made, whilstin the energised condition the contacts t and `8 are made, the operationbeing a make-before-break operation insofar as these contacts areconcerned.

The footplate 30' carries a pair of opstanding pillars 31 and 32, which,by means of insulating spacers 33, serve to mount the two 'thermalswitches. Each switch comprises along relatively broad limb 34 which issecured on the posts 31 and `32 and which is unitary with a shorternarrower limb 3S, the two limbs being joined together to form a U andbeing composed of identical bi-rnetallic material so that thearrangement is self-compensating for ambient temperature. In FIGURE 2,the upper switch is the `switch HM whilst the lower switch is the switchHL.

As can be seen from FIGURE 2i, the limb 315 of the switch HM has its endpositioned between a pair of xed contacts forming the contacts 1e.- and15, such contacts being carried by bent arms 3'/ mounted upon the pillar31 and each uni-tary with a plate 38 extending to the pillar 32 so thatelectrical connections can be made to the remote ends of such plates.The arm 35 Vitself carries the contact 13. The end of the arm 35 isengaged by a C-type spring 39 which has its end secured immediatelybelow the head of a set screw titl' which is adjustable in a plate 41.Ilt will be understood that movement of the set screw 4t) in the plateil changes the effective angle of the spring 39 and thus controls itsoperation.

A heater l2 is located about the limb 35.

The operation o the switch HM is that, as the heater 42 is energised,the limb 35 bows relatively to the limb 34 against the action or" thespring 39' so that, as soon as the action of the spring is overcome, thearm 3S snaps into the position in which the contact 13 makes with thecontact 1d. However, the spring 39 does not go over dead centre and sowhen the heater fili cools down the arm 35' may snap back into theposition shown in the drawings in which the cont-acts 13 and 1S aremade.

The switch HL is substantially identical in construction to the switchHM except that the second `contact (corresponding to the contact 1d) isarranged differently. This second contact, which forms the contact 5, isconstituted by a set screw mounted in a plate i3 carried by a resilientarm 44 which is located in a slot in a guide member 45, such guidemember 45 being mounted upon the lstud 31 and the resilient arm t4 beingmounted upon the two studs 31 and 32. The arrangement is that as the arm35 of the switch HL is heated it acts against its spring 39 until it`overcomes the action of this spring and it then moves over thedead-centre position soi as to make with the Contact 3i. Since thespring 39 has moved over the dead-centre position, the switch HL doesnot reset on cooling and must be manually reset by operation of the endof the resilient arm 44 which can be moved in the guide l5 so as to urgethe arm 3S upwardly (as seen in FIGURE 2) and over the dead-centreposition to engage with the contact 2. When urged in this way, the arm3S snaps into the position shown in the drawing and remains there whilstthe contact 3 restores itself under the influence of its resiliencytothe position shown. Thus, although the switches HM and HL areconstructionally almost identical, they differ in that the switch HM`works entirely on one Vside of the dead-centre position and is thusself restoring, whilst the switch HL works on both sides of thedead-centre position and must bemanually reset.

In the circuit described above with reference to FIG- URE 1, it ispossible that contacts 4 and' 5 may fail to make when relay R pulls in.The arrangement `of FIG- URE 1 would then operate normally except that,should flame not be established or should the flame fail 'during a runthe switch of the delay device controlling lock-out would fail tooperate and this circumstance would be potentially dangerous.

To avoid this risk the circuit or' FIGURE l may be moditied as shown inFIGURE 3. In the circuit shown in FIGURE 3 the `delay device controllingthe motor M is provided with two heaters HM1 and HMZ, the heater HMIbeing connected between contacts 9 and 13 and heater HMZ being connectedbetween resistors RM and VR. The contacts 4, 5, 6, 3, 11 and 12 of therelay R `are connected as they are in FIGURE 1 but contact 7 of therelay R is connected to Contact 10 of the relay via lead 28.Furthermore, contact 15 of the motor control delay device is not used inthe circuit.

When the thermostat Th makes to call for heat the relay R is energised,as in the circuit of FIGURE 1, via resistor RD, bridge rectier BR,contacts 7 and 8, the 'heater HL of the delay vdevice controlling lockout and resistor VR. On picking up the relay R completes a circuit fromlead 23` via the heater HMI, contacts 9, 10', lead 28 and the seriesparalled circuit having as onebranch the heater HL and resistor VR inseries, as a second branch the contacts 4, 5, leads 26 :and 27 and motorM in series and as .a third branch resistor RM and heater I-IMZ inseries. The resistance of heater HM1 is, however, suilciently high topre-vent operation of the motor M and also to prevent the temperaturesof heaters HL and HMZ rising above respective predeter-` mined values.

The resulting current iowing through heater HMI causes contacts 13 andle to make after heater HMl has been energised for a pre-ignition periodand the making of these contacts fully energises the motor M. The makingcf contacts 13, 14 also fully energises heater HMZ via resistor RH tocause contacts 13 and 14 to ybe held closed after relay R releases whendarne is established and heater HMl becomes -de-energised 'as :aconsequence.

Should contacts 4 and 5 in the circuit of FIGURE 3 fail to make whenrelay R picks up initially an energising circuit for the lock-out heaterHL is completed from lead 23 vi-a heater HMI, contacts 9, 10, lead 28,heater HL and resistor VR. The values ofthe resistive elements in thisenergising circuit are so chosen that the current flowing therein willcause the contact 1 of the lock-out delay device to operate beforecontact 13 of the motor control delay device operates. Consequently,instead of the burner lbeing lit as it would be with the circuit of FIG-URE 1, the circuit of FIGURE 3 assumes the `lock-out condition ifcontacts 4 and 5 fail to make when relay R picks up originally.

We `claim:

l. A fuel control means for a burner comprising fuel supply means; fuelignition means; a thermostat responsive to a temperature which isincreased -by operation of said burner; a relay having a coil and first,second and third -switch means; a first circuit for energising saidcoil, the first circuit including the thermostat and being energised tooperate the relay in response to the lthermostat calling for heat; atirst delay device comprising a first switch, ia first lactuator andfirst heater means for heating the first actuator to operate the firstswitch; a second circuit for energising the fuel supply means, thesecond circuit including the first switch and being fully energised when.the rst switch is operated; a third circuit for energising the fuelignition means, the third circuit including the third switch means andbeing energised when the relay is oper-ated; circuit means forenergising the iirst heater means, the circuit meansincluding thesec-ond switch means and the first switch, the circuit means being fullyenergised when the relay is operated and ythe first switch is unoperatedand lbeing energised to maintain the first switch operated when therelay and the first switch are operated; `a manually resettable seconddelay device comprising a second switch, a second actuator and secondheater means for heating the second actuator to operate the lsecondswitch; a. fourth circuit for energising the second heater means, thefourth circuit including the first switch means and the first `switchand lbeing energised when the relay and the first lswitch are operated,the second switch being connected in controlling relation to andoperative to de-energise all the circuits and the circuit means, andmeans responsive to said fuel being ignited to reduc/e the energisationof the coil to release the relay.

2. A fuel control means according to claim 1 comprising a resistiveelement connected to the first switch means and wherein the firstcircuit includes the first switch means and the first switch meansconnects the second heater means in the first circuit initially and`substitutes the resistive element for the second heater means in thefirst circuit when the relay is oper-ated.

3. A fuel control means according to claim l wherein the rst heatingmeans comprises two heater elements; the circuit means comprise a fifthcircuit for energising one of said heater elements and a sixth circuitfor energising the other of said heater elements, the iift-h circuitincluding the second switch means and the second heater means and beingenergised to [operate the iirst switch when the relay is operated, thesixth circuit including the first switch and being energised uponoperation of the first switch to maint-ain the rst switch operated, therelative resistances of the iirst heater element and the second heatermeans being such that when they carry the same current the second switchoperates before the first switch.

4. A fuel control means according to claim l wherein the meansresponsive 4to ignition vof the `burner is a photoresistive cellconnected to provide when illuminated `a current path in parallelrelation to the coil.

References Cited in the file of this patent UNITED STATES PATENTS1,910,721 Taylor et al May 23, 1933 1,961,802 Taylor .lune 5, 19342,216,748 Lindemann Oct. 8, 1940 2,409,492 Jones Oct. 15, 1946 2,772,727Schell Dec. 4, 1956

1. A FUEL CONTROL MEANS FOR A BURNER COMPRISING FUEL SUPPLY MEANS; FUELIGNITION MEANS; A THERMOSTAT RESPON SIVE TO A TEMPERATURE WHICH ISINCREASED BY OPERATION OF SAID BURNER; A RELAY HAVING A COIL AND FIRST,SECOND AND THIRD SWITCH MEANS; A FIRST CIRCUIT FOR ENERGISING SAID COIL,THE FIRST CIRCUIT INCLUDING THE THERMOSTAT AND BEING ENERGISED TOOPERATE THE RELAY IN RESPONSE TO THE THERMOSTAT CALLING FOR HEAT; AFIRST DELAY DEVICE COMPRISING A FIRST SWITCH, A FIRST ACTUATOR AND FIRSTHEATER MEANS FOR HEATING THE FIRST ACTUATOR TO OPERATE THE FIRST SWITCH;A SECOND CIRCUIT FOR ENERGISING THE FUEL SUPPLY MEANS, THE SECOND WHENTHE FIRST SWITCH IS OPERATED; A THIRD CIRCUIT FOR ENERGISING THE FUELIGNITION MEANS, THE THIRD CIRCUIT INCLUDING THE THIRD SWITCH MEANS ANDBEING ENERGISED WHEN THE RELAY IS OPERATED; CIRCUIT MEANS FOR ENERGISINGTHE FIRST HEATER MEANS, THE CIRCUIT MEANS INCLUDING THE SECOND SWITCHMEANS AND THE FIRST SWITCH, THE CIRCUIT MEANS BEING FULLY ENERGISED WHENTHE RELAY IS OPERATED AND THE FIRST SWITCH IS UNOPERATED AND BEINGENERGISED TO MAINTAIN THE FIRST SWITCH OPERATED WHEN THE RELAY AND THEFIRST SWITCH ARE OPERATED; A MANUALLY RESETTABLE SECOND DELAY DEVICECOMPRISING A SECOND SWITCH, A SECOND ACTUATOR AND SECOND HEATER MEANSFOR HEATING THE SECOND ACTUATOR TO OPERATE THE SECOND SWITCH; A FOURTHCIRCUIT FOR ENERGISING THE SECOND HEATER MEANS, THE FOURTH CIRCUITINCLUDING THE FIRST SWITCH MEANS AND THE FIRST SWITCH AND BEINGENERGISED WHEN THE RELAY AND THE FIRST SWITCH ARE OPERATED, THE SECONDSWITCH BEING CONNECTED IN CONTROLLING RELATION TO AND OPERATIVE TODE-ENERGISE ALL THE CIRCUITS AND THE CIRCUIT MEANS, AND MEANS RESPONSIVETO SAID FUEL BEING IGNITED TO REDUCE THE ENERGISATION OF THE COIL TORELEASE THE RELAY.